1. Field of the Invention
This invention relates to pulse radar apparatus and to the displaying of information from such apparatus.
2. Prior Art
It is the common practice to display radar information from a pulse radar receiver using a brightness modulated cathode ray tube. Plan position displays produced in this way are widely used, for example, in marine radars as they provide a form of display which is readily understood by the observer. In marine radars, it is generally necessary to make provision for switching the time base speed to any one of a number of different values to give different range scales for the display.
It is known to digitize the radar video signal from a pulse radar receiver by repetitively sampling the video signal and determining, for each sample, whether or not a reflected pulse signal is present. Such digitized radar information can be processed using digital data processing techniques. Such digital processing of radar signals is widely used, for example, for aircraft control purposes.
However, in marine radar apparatus, it is generally necessary to provide a display which is switchable, in steps, to cover many different range scales. It is sometimes necessary to have a display having a large area and commonly a display of up to 48 nautical miles is provided. At the other extreme, a display covering only a small area, e.g. extending to only a fraction of a mile might be required. It has been the conventional practice on marine radars to effect the scale-changing of the display by switching the time-base speed of the time-base scan generator for a cathode-ray display tube. When the time-base speed is changed, the brightness of the display changes. Also it is the common practice to lengthen the duration of the transmitted pulse on longer range displays to improve visibility of the display.